Apparatus for measuring alignment characteristics of front and rear wheels



April 19, 1955 CARR|GAN 2,706,427

APPARATUS FOR MEASURING ALIGNMENT CHARACTERISTICS OF FRONT AND REARWHEELS Original Filed April 3, 1946 12 Sheets-Sheet 1 k INVENTOR. NTRACY GARRIGAN April 19, 1955 11 ARR|GAN 2,706,427

APPARATUS FOR MEASURING ALIGNMENT CHARACTERISTICS OF FRONT AND REARWHEELS Original Filed April 3, 1946 12 Sheets-Sheet 2 N Nn INVENTOB.TRACY GARRIGAN April 19, 1955 c R 2,706,427

APPARATUS FOR MEASURING ALIGNMENT CHARACTERISTICS OF FRONT AND REARWHEELS Original Filed April 3, 1946 12 Sheets-Sheet 3 uvmvrox. TRACYOARRIGAN April 19, 1955 T. CARRIGAN 2,706,427

APPARATUS FOR MEASURING ALIGNMENT CHARACTERISTICS OF FRONT AND REARWHEELS April 19, 1955 1' cARRlGAN 4 2,706,427

APPARATUS FOR MEASURING ALIGNMENT CHARACTERISTICS OF FRONT AND REARWHEELS Original Filed April 3, 1946 12 Sheets-Sheet .5

INVEN TOR. TRACY GARRIGAN Aprll 19, 1955 cARRlGAN 2,706,427

APPARATUS FOR MEASURING ALIGNMENT CHARACTERISTICS v v OF FRONT AND REARWHEELS Original Filed April 3, 1946 12 Sheets-Sheet 6 INVENTOR. TRACYcAamqAu ATTOZ/VEV 2,706,427 APPARATUS FOR MEASURING ALIGNMENTCHARACTERISTICS 12 Sheets-sheaf 7 INVENTOR.

TRACY CARRIGAN Aprll 19, 1955 CARRHGAN 2,706,427

APPARATUS FORMEASURING ALIGNMENT CHARACTERISTICS OF FRONT AND REARWHEELS Original Filed April 3, 1946 12 Sheets-Sheet 8 INVENTOR.

TRACY CARRIGAN BY MW HI WZ J.

April 19, 1955 T. CARRIGAN 2,706,427

APPARATUS FOR MEASURING ALIGNMENT CHARACTERISTICS OF FRONT AND REARWHEELS Original Filed April 3. 1946 12 Sheets-Sheet 9 INVENTOR. TRACYGARRIGAN Apnl 19, 1955 r. CARRIGAN 2,706,427

APPARATUS FOR MEASURING ALIGNMENT CHARACTERISTICS OF FRONT AND REARWHEELS Original Filed April 3, 1946 12 Sheets-Sheet 10 mmvro TRACYOARRIGAN #ltw e ww Aprll 19, 1955 ARR|GAN 2,706,427

APPARATUS FOR MEASURING ALIGNMENT CHARACTERISTICS OF FRONT AND REARWHEELS Original Filed April 3, 1946 12 Sheets-Sheet 11 INVEN TOR.

OARRIGAN P30 MOP Z MOF NZMU 7: MO? .50 MOP Arrawvay 2,706,427 ACTERISTICS l2 Sheets-Sheet 12 U tM-LiJOC T. CARRIGAN APPARATUS FORMEASURING ALIGNMENT CHAR OF FRONT AND REAR WHEELS Original Filed April3, 1946 NW .ONbN

April 19,

INVENTOR.

TRACY OARRIGAN BY qwmfi. Hw w'iz ATTUP/VEY United States PatentAPPARATUS FOR MEASURING ALIGNMENT CHARACTERISTICS OF FRONT AND REARWHEELS Tracy Carrigan, Lansing, Mich., assignor to chinery and ChemicalCorporation, San Jose, corporation of Delaware Food Ma- Calif., a

6 Claims. (Cl. 88-14) This invention relates to the art of checking thealignment of vehicle wheels.

It is an object of this invention to provide a novel apparatus forchecking alignment characteristics of dirigible vehicle wheels.

It is another object of the invention to provide an apparatus foraccomplishing the foregoing object optically and indicating readilyunderstood by unskilled persons, and particularly by the averageautomobile owner.

The present invention is an improvement on the optical wheel alignerdisclosed in the joint application for U. S. Letters Patent, Serial No.571,716 filed by myself, Herbert G. Holmes, and Clyde A. Shoemaker onJanuary 5, 1945, Patent 2,470,090 granted May 17, 1949. In that wheelaligner, optical units were disposed for sliding movement laterallytowards and away from the front wheels of the automobile being testedand the characteristics of these wheels were checked by these units andindicated on charts optically projected thereby on screens set up infront of said vehicle. For these units to function properly, it isnecessary for them to be located in a particular spaced relation withmirrors mounted on said wheels and, in said prior invention, thisadjustment was accomplished for each unit with reference to an opticalphenomenon which resulted from shifting said unit towards or away fromthe mirror on the adjacent wheel. While this phenomenon for allpractical purposes accurately indicated when the correct positioning ofthe optical units had been accomplished at the start of the test of apair of front dirigible wheels of a vehicle, excessive camber in thesewheels caused a variation in said phenomenon when said wheels were beingchecked for caster which tended to confuse the operator (unless hestopped to think) as it gave the appearance of indicating that theoptical units were out of their proper positions.

It is another object of the present invention to provide an opticalwheel aligner in which the proper spacing of the optical units from thewheel mirrors is accomplished optically without the optical phenomenoninvolved being distorted during any part of the test by the amount ofcamber present in the wheels being tested.

The manner of accomplishing the foregoing objects, as well as furtherobjects and advantages, will be made manifest in the followingdescription taken in connection with the accompanying drawings in which;

Fig. 1 is a perspective view of a preferred embodiment of the apparatusof the invention.

Fig. 2 is a perspective view of an automobile supported on the apparatusshown in Fig. 1 and in the process of having the alignment of the fourwheels thereof checked by said apparatus.

Fig. 3 is a close-up perspective view of the rear left wheel of saidautomobile while the alignment thereof is being checked by saidapparatus.

Fig. 4 is a vertical sectional view through the clutchclamp of thedevice preferably employed to mount mirrors on the wheels being tested.

Fig. 5 is a plan view of the left hand optical unit of the apparatus ofthis invention with the housing in section to show the internalconstruction.

Fig. 6 is a side elevational view of Fig. 5 with the housing in section.

the results so that these may be seen and (ill Fig. 7 is an enlargedcross sectional view of the film slide of the chart projector of theinvention taken on the line 77 of Fig. 5.

Fig. 8 is an enlarged longitudinal sectional view of the rear beam maskadjuster of the invention and is taken on the line 8-8 of Fig. 6.

Fig. 9 is a front elevational view of one of the front wheel mirrors ofthe invention.

Fig. 10 is a front elevational view of the frame of said front wheelmirror.

Fig. 11 is a plan view of said front wheel mirror.

Fig. 12 is a cross sectional view taken on the line 1212 of Fig. 11.

Fig. 13 is a plan view of said front wheel mirror frame partly brokenaway to illustrate the inner construction.

Fig. 14 is a plan view of the left rear wheel mirror of the invention.

Fig. 15 is a front elevational view of Fig. 14.

Fig. 16 is a cross sectional view taken on the line 1616 of Fig. 14.

Fig. 17 is a plan diagram of the operation of the left hand optical unitof the apparatus.

Fig. 18 is a side elevational view of Fig. 17.

Fig. 19 is a plan diagram of the invention being used to check thealignment of the rear wheels of an automobile in which said alignment isfound to be perfect.

Fig. 20 is a diagram of the left and right drive wheel charts producedby said apparatus in the check illustrated in Fig. 19 and indicatingperfect rear wheel alignment.

Fig. 21 is a plan diagram of the invention being employed to check thealignment of the drive wheels in which the differential housing is foundto be cocked.

Fig. 22 is a diagram of the left and right drive wheel charts indicatingthe condition illustrated in Fig. 21.

Fig. 23 is a plan diagram of the invention being employed to check thealignment of the drive wheels of an automobile in which the differentialhousing is sprung so that the axes of rotation of the wheels on each endof this are out of alignment with each other in a horizontal plane.

Fig. 24 is a diagram of the left and right drive wheel charts producedby the invention and revealing the condition illustrated in Fig. 23.

Fig. 25 is a rear elevational diagram of an automobile being checked andshowing the differential housing sprung vertically so that the axes ofrotation of the wheels on opposite ends thereof are out of alignmentwith each other in a vertical plane.

Fig. 26 is an enlarged diagram of the left and right bubble levelsprovided on the drive wheel mirrors of the apparatus of the invention asthese are disposed by the condition illustrated in Fig. 25.

Fig. 27 is a side elevational diagram showing the paths of light beamsemployed in this invention for checking the alignment of the rear drivewheels of a vehicle.

Fig. 28 is a diagrammatic view illustrating the camber chart employed inthe invention.

Fig. 29 is a diagrammatic view illustrating the caster chart employed inthe invention as set during the initial cocking of the left front wheelof an automobile being checked for caster.

Fig. 30 is a view similar to Fig. 29 illustrating the reading of casteron said caster chart after the reverse cocking of said left front wheel.

Referring specifically to the drawings, the preferred embodiment of theapparatus of the invention is indicated therein by the numeral 30 andincludes two apparatus sections, a left hand section 31 and a right handsection 31' which are reverse duplicates of each other so that adetailed disclosure and description of one will suffice for both. Onlythe left hand section is thus disclosed and described. Whateverreference is made to the right hand apparatus section 31 will,therefore, be made by using the reference numerals of correspondingparts in the left hand section 31, with prime attached.

The two apparatus sections 31 and 31' are mounted on a testing floor inparallelism as shown in perspective in Fig. 1 so that a vehicle to betested can be driven onto and off of the apparatus, as shown in Fig. 2,under its own power.

The left hand apparatus section 31 includes a wheel track 33 and anapproach ramp 34, which are supported on legs 35 and a turntable base36, at the front end of the track, which carries a turntable 37 and afront wheel bumper 38. Extending between and supported on the turntablebases 36 and 36 is a double jack beam 39 which supports jacks 40 and40'.

Formed integral with and extending laterally from the turntable base 36is a horn which embodies an optical unit slideway 46 on which an opticalunit 47 is slideably mounted.

The slideway 46 is embodied in an upper wall of the horn 45. This wallhas a central slot 48 (Fig. 6) on opposite sides of which are provided aflat rail 49 and a double bevel rail 50. Adjacent the slot 48 and formeddownwardly from the upper wall of horn 45 are a pair of internal rails51. The slot 48 and the rails 49. 50 and 51 are all horizontal, parallelto one another, and perpendicular to the vehicle Wheel track 33.

The optical unit 47 includes a pedestal 52 which is formed as shown inFig. 6 to fit the rails 49 and 50 so that the unit 47 is slideable onthese rails. To hold the unit 47 from being accidentally dislodged fromsnug contact with these rails, the pedestal 52 has a hold-down rod 53which extends downwardly through the slot 48 and carries a yoke 54having rollers 55 which are yield ably held upwardly against the rails51 by a spring 56 coiled about the rod 53 between the yoke 54 and a nut57 on the lower end of the rod.

Provided on the upper end of the pedestal 52 is a shaft 60 which isgripped by clamps 61 of a unit floor 62, thereby supporting this flooron shaft 60 so that the floor may be adjusted about this shaft ifdesired. The axis of shaft 60 is parallel with rails 49 and 50. Fixed onone end of the shaft 60 is an arm 63, the upper end of which is providedwith a stub-shaft 64, this carrying on its outer end a handle 65 formanipulating the unit 47. The lighting circuit of this unit iscontrolled through a switch 66 provided on handle 65.

Mounted on the unit floor 62 are two projectors 67 and 68. The projector67 rests directly on the floor and performs the function of projectingthe chart onto a screen 70 which, for convenience, is mounted in adFarkeined recess 71 provided in a screen cabinet 72 (see The projector67 includes a frame 75 supporting an electric lamp 76, an opticalcondenser 77, a chart slide box 78, and a projecting lens element 79which may be of the type known as Eastman, Model-I-KodaslideProjector-F3.7-4" Focus.

As shown in Fig. 7, the slide box 78 provides a vertical slideway 80 inwhich a film slide 81 having a rack 82 may he slid upwardly ordownwardly by engagement of a pinion 83 with this rack. The pinion 83 isfixed on a shaft 84, the latter being mounted in suitable bearingsprovided on the frame 75 and extending rearwardly to terminate in aknurled head 85. Fixed on the film slide 81 by screw 86 is an eccentricstop 87 which engages the slide box 78 when the slide 81 is in itsdownwardmost position. By selecting the rotational position in which thestop 87 is snugged against the slide 81, the proper downwardmostposition of the latter may be determined within a relatively smallmargin of adjustment. The slide 81 is provided with a camber chart film89, a drive wheel chart film 90 and a caster chart film 91. In thesefilms as shown in Fig. 7, the representations of the charts are invertedso that they will appear right side up when projected.

By manipulation of the knurled head 85, the slide 81 may be elevated ordepressed in the slideway 80 to selectively project onto the screen 70 achart image from one of the films 89, 90 or 91 or to adjust the verticalposition of one of these charts on said screen.

The projector frame 75 has transverse walls 92 and 93 which support atelescope 94, the inner end of which has a collar 95 carrying areflector 96, the latter having a central aperture 97 through whichlight rays may be emitted rearwardly from the lamp 76 (Fig. 8).

Also provided on the collar 95 is a flat spring 98 bent as shown in Fig.8 and having a hole 99 disposed opposite the reflector hole 97 andengaged by a screw 100 for adjusting the position of a mask 101 providedon the spring 98 with respect to the filament 102 of the lamp 76. Themask 101 has a cruciform aperture 103 which, by manipulation of thescrew 100, is adapted to be disposed coaxially with respect to thetelescope 94 so that a beam of light 105 will be projected rear- Wardlythrough this aperture along the extended axis of the telescope. Providedon the rear end of the telescope 94 is a collar in which is mounted aprism lens 111 which causes the beam 105 to be projected rearwardly astwo beams 112 and 113 (Fig. 27).

These beams are disposed in the same vertical plane and may be referredto for purposes of distinguishing them as primary beam 112 and secondarybeam 113. The primary beam is preferably projected horizontally and thebeam 113 inclined upwardly about 2 from horizontal (Fig. 27).

The projector 68 is mounted on a table 116 provided on floor 62 so as tobe located at a higher level than and laterally displaced from theprojector 67 (Figs. 5, 6, 17 and 18). The projector 68 includes a frame117 in which is mounted an electric lamp 118, a reflector 119, acondenser element 120 which is retained in place by a spring 121, and across hair beam mask 122. The function of the projector 68 is to projecta beam of light through the mask 122 which will ultimately beintercepted by the screen 70 in the form of a cross hair image in amanner and for a purpose which will be made clear hereinafter.

Fixed on the optical unit floor 62 is a table 125 (Figs. 5 and 6) havingmounted thereon a mirror 126, a lens 127 and a mirror 128. Also fixed onthe floor 62 is a frame 129 carrying a relatively large mirror 130 andalso having mounted thereon a locator lamp 131, a locator beam mask 132,and a mirror 133. Fixed on the floor 62 is a bracket 134 carrying alocator beam lens 135. The optical unit 47 is supplied with electricitythrough suitable conductors (not shown) for energizing the lamps 76,118, and 131, on a single circuit controlled by the switch 66.

Unit 47 is enclosed by a suitable streamlined housing having a loweraperture 141 for receiving the pedestal 52, a front aperture 142 coveredby a window 143, and a side aperture 144.

The apparatus section 31 of the invention also includes a dirigiblewheel mirror and a drive wheel mirror 151 which, when performing themethod of the invention, are supported on the left dirigible and drivewheels respectively of a vehicle, the alignment characteristics of whichare being checked. I prefer to employ for the purpose of so mountingsaid mirrors a wheel mirror mount 152, the structure of which is fullydisclosed in the application for U. S. Letters Patent of Herbert G.Holmes, Ser. No. 614,267 filed September 4, 1954, on a Wheel MirrorMount, Patent 2,475,502 granted July 5, 1949.

The mount 152 includes a pair of parallel slide bars 153, adjacent endsof which are fixed in a cross member 154 having rim engaging jaws 155and 156. Slideable on the opposite ends of the bars 153 is a clutchclamp 157 having a jaw 158. The jaws 155 and 156 and 158 have innerfaces which lie in a plane parallel with the plane of the bars 153 andare adapted to be brought to bear against the outer edge of a wheel rimsuch as the rim 159 in Fig. 3. Each of these jaws has a tooth 160,preferably formed of a hardened screw, which, when the jaws are sopositioned, lies outside of the rim 159. The clutch 157 has a clutchmechanism 162 which may be actuated by a handle 163 to grip the bars 153and,

upon further movement of the handle 163, shift the clutch clamp 157inwardly on these bars.

The mechanism 162 includes a hollow body 164, with which jaw 158 isformed integral. The body has vertically spaced walls 165 and 166through aligned holes in which the bars 153 slide. Journalled in a hole167 in wall 166 perpendicular to the plane of the bars 153 is a camshaft 168 having a notch 169, this shaft carrying the handle 163.Disposed between walls 165 and 166, having holes 170 through which bars153 normally loosely slide, and yieldably held downwardly by springs171, is a locking dog 172, the inner end 173 of which turns down andbears against the shaft 168 opposite the notch 169 therein. Normally thedog end 173 rests in notch 169 and bars 153 are free to slide throughholes 170. When the shaft 168 is rotated by the handle 163 the dog 172is first cocked into a gripping relation with bars 153. Further rotationof shaft 168 then shifts the clamp 157 along bars 153 toward the centerof the rim 159, thereby embedding the teeth 160 of jaws 155, 156 and 158in the metal of the rim and securing the mount 152 to said rim.

Slideably mounted on the bars 153 between the member 154 and clutchclamp 157 is a device supporting slide 175 having a socket 176, the bore177 of which is disposed at right angles to the plane of the slide bars153. The slide 175 has spring and ball detents 178 (Figs. 11 and 12)which frictionally bear against the slide bars 153 and prevent slide 175from being accidentally shifted from a position in which it has beenplaced on said bars.

The dirigible wheel mirror 150 includes a frame 179 having a hub 180,the latter having a bore 181 (Fig. 13). Trapped in the bore 181 by a cap182 is a double ball bearing 183 into which a shaft 184 extends, thelatter being held in said bearing by a plate 185 so that this bearingabuts against a shoulder 186 formed on said shaft. Beyond the shoulder186 the shaft 184 is of proper diameter to snugly fit the bore 177 ofthe slide 175 and is held therein as by a set screw 187.

Secured on the frame 179 by clips 190 are a central mirror 191 and wingmirrors 192 and 193, the Wing mirrors being inclined backwardly atrelatively to the central mirror 191. The central mirror 191 is disposedin a plane which is perpendicular to the axis of the shaft 184. Providedon the frame 179 is a counterbalance weight 194 which lowers the centerof gravity of the mirror 150 so that this always remains upright inplumb fashion regardless of the rotation of the shaft 184 on which themirror is mounted. When this shaft is disposed horizontally, the mirror191 which is perpendicular to the shaft is disposed vertically and thewing mirrors 192 and 193 are so related to the central mirror 191 thatthey are at this time also disposed vertically.

Enclosing the frame 179 of the mirror 150 is a hous ing 195 havingbrackets 196 by which it is secured to the frame. The housing 195 alsohas a front opening 197 through which the mirrors 191, 192 and 193 areexposed to view, this opening being surrounded and the mirrors framed bya rubber moulding 198 which is mounted on the edge of the housingbordering said opening.

The drive wheel mirror 151 (Figs. 3, 14, 15 and 16) includes a shaft 200having calibration marks 201 cut therein at regular intervals for apurpose to be made clear hereinafter. This mirror also includes a framestructure 202 which is preferably stamped of light sheet metal and isprovided with spaced holes 203 through which the shaft 200 slideablyextends and an apertured, internally-threaded ear 204 which is adaptedto receive a thumb screw 205 to permit the latter to be screwed againstthe shaft 200, thereby locking the mirror 151 in any desired position onthis shaft. Mounted on the frame 202 in a plane parallel with the shaft200 1s a mirror 206, this being supported by clamps 207 provided on theframe 202. Enclosing the frame 202 and mirror 206 is a housing 208, thelatter having suitable apershaft 200 and screw 205 extend. It also hasan upper aperture 209 just beneath which a spirit level 210 is mountedon the frame 202. This level is provided with suitable calibrations (seeFigs. 14 and 26) for measuring the inclination of the shaft 200 relativeto horizontal.

The housing 208 also tures through which the has a window opening 212which is framed by a rubber moulding 213 mounted on the housing edgeadjacent this opening. Secured to the outer surface of the housing 208just beneath the window opening 212 is a calibrated screen 214 havingvertical calibrations 215 identified by numbers 216 disposed along theupper edge of the screen.

Operation The apparatus shown in the drawing and described hereinaboveis adapted to be employed in the performance of the method of theinvention to check the alignment characteristics of the front ordirigible wheels 220 and 220' of an automobile 221 and, in the sameoperation, check the alignment characteristics of the drive or rearwheels 222 and 222 of said automobile.

In preparation for performing this checking operation the automobile 221is driven upwardly over the ramps 34 and 34' onto the tracks 33 and 33until the front or dirigible wheels 220 and 220 rest on the turntables37 and 37' free from contact with the bumpers 191 is greater or less 38and 38. The front or dirigible wheels 220 and 220' now have wheel mounts152 and 152' applied thereto with mirrors 150 and 150 carried on saidmounts as clearly shown in Figs. 2, l0 and 11.

Rear drive wheels 222 and 222 are also fitted with identical mounts 152and 152, with the sockets of the latter supporting shafts 200 and 200'and with the mirrors 206 and 206' mounted on said shafts so that theindicia 201 and 201 indicates that these mirrors are equally spacedoutwardly from the planes of the outer edges of the rims of the wheels222 and 222. By loosening thumb screws 205 and 205, the mirrors 206 and206 are rotated into substantially vertical positions, the planes of themirrors 206 and 206 being, of course perpendicular respectively to theplanes of the wheels 222 and 222'.

The operator now snaps on the switch 66, illuminating the lamps in theoptical unit 47. This causes the projector 67 to project a chart ontothe screen 70 and at the-same time project beams 112 and 113 rearwardly.As shown in Figs. 3 and 27, the primary rearward beam 112 impinges onthe screen 214 of the drive wheel mirror 151 to form a cruciform beamimage 223. The secondary rearward beam 113 is inclined upwardly from theprimary beam 112 just enough to impinge upon the mirror 206 so as to bereflected therefrom onto the screen 70 to form a cruciform beam image224 (Figs. 22 and 24).

As before noted, the two vertical planes, one of which containsleft-side rearward light beams 112 and 113 and the other of whichcontains the corresponding rightside rearward beams 112' and 113, areparallel at all times by virtue of the mounting and adjustment of theoptical units 47 and 47'. Correction to maintain this parallelism isaccomplished by adjustment of the screws and 100' (see Fig. 8). Itshould also be noted that beams 112 and 112' are parallel and beams 113and 113 are parallel.

For the apparatus 30 to perform the method of the invention, it ispreferable that each of the optical units 47 and 47 be located a certainpredetermined distance laterally from the adjacent dirigible wheelmirror. This correct location of the optical units is accomplishedseparately and in the same way for each of these units.

In the case of unit 47, the latter is pushed or pulled manually, bygrasping the handle 65, to slide the unit on its rails 49 and 50 towardor away from the wheel mirror 150, until the unit is correctly locatedwith respect to said mirror. The operator is able to know that the unit47 is thus correctly located by observation of the relation betweencertain images projected by this unit onto the screen 70, as will now beexplained.

When the lamps 76, 118 and 131 are energized, the projector 68 projectsa beam 225 through the mask 122 which impinges against the mirror 126(Figs. 5, 17 and 18). From this mirror it is reflected through the lens127 which suitably refracts the rays of this beam to prevent theirunduly spreading, the beam continuing into contact with the centermirror 191 so that the reflection of this beam from mirror 191 returnsoutwardly against the mirror 130 from which it is reflected onto thescreen 70 to form a cross hair image 226.

The lamp 131 projects a beam of light 227 through a cruciform opening inthe mask 132 against the mirror 133 from which this beam is reflectedthrough the lens 135 against the central dirigible wheel mirror 191 fromwhich this beam is reflected onto mirror 128 and thence onto the screen70 where it forms a cruciform locator image 228. As may be noted fromFigs. 6 and 18, the cross hair beam 225 and the locator beam 227, justdescribed, lie in the same horizontal plane as they travel on their wayto impingement against the mirror 191. The various elements utilized inprojecting these beams are so related that the point in said plane atwhich said beams meet, lies in the plane of the reflecting surface ofthe mirror 191 when the optical unit 47 is properly located laterallyfrom the mirror 191 for performing an alignment checking operation.

The mirrors 128 and 130 by which the cross hair beam 225 and locatorbeam 227 are reflected onto the screen 70 are so angled that when theoptical unit 47 is thus properly related to the mirror 191 as shown infull lines.

in the diagram of Fig. 17, the cross hair image 226 and the cruciformlocator beam image 228 are located on the screen 70 in verticalalignment with each other. When the spacing between the optical unit 47and the mirror than the proper distance, these two images are out ofvertical alignment. This is indicated in Fig. 17 by the broken linepaths of beams 225 and 227 which occur when the spacing between themirror 191 and the optical unit 47 is greater than the desired distance.

It is thus clear that to properly relate the unit 47 to its dirigiblewheel mirror 150, the operator merely shifts it along its slideway 46until the images 226 and 228 on the screen 70 come into verticalalignment. The proper spacing of the optical unit 47 from the mirror 191having been thus accomplished, the operator now repeats this procedureon the right hand side of the automobile 221 to correctly locate theoptical unit 47' relative to the wheel mirror 191'.

The vertical parallel planes containing the left-side rearward beams 112and 113 and the right-side rearward beams 112' and 113 are nowequidistant laterally from the point 229 (Fig. 19) on the fore and aftaxis 230 of the automobile where this axis intersects with the verticalplane passing through the centers of dirigible wheels 220 and 220'. Themethod of the invention next contemplates a relative rotation aboutpoint 229 in a horizontal plane between the automobile 221 and therearward beams 112 and 112' until the fore and aft axis 230 of theautomobile and these beams are brought into parallelism.

While the optical units 47 and 47 may be made adjustable to bring aboutthis parallelism, it is preferred to accomplish this by shifting therear end of the automobile 221 to one side or the other. The amount, ifany, which the fore and aft axis of the automobile is out of parallelismwith the beams 112 and 112' is determined by observing the location ofthe cruciform image 223 of beam 112 on the mirror screen 214 and thelocation of the image 223' of beam 112' on the corresponding screen 214'on the right hand side of the automobile 221. Where these images are notlocated in exactly the same lateral relation to the indicia of these twoscreens, the rear end of the automobile is shifted laterally until theyare.

To prevent any error being introduced into the read ings for thealignment characteristics of the front wheels 220 and 220 by one ofthese being bent out of perpendicularity with its axis of rotation, thefront end of automobile 221 is now lifted by the jacks 40 and 40'. Thewheels 220 and 220' are then rotated and any wobble indicated by acircular movement of cross hair images 226 and 226 on the screens 70 and70' is noted. These wheels are now halted with the images 226 and 226 atpoints disposed half way between upper and lower extremes of theircircular paths and lowered onto turntables 37 and 37'. These circularpaths will hereafter be referred to as wobble circles. While notnecessary to secure accurate results the front wheels 220 and 220' are,for the sake of uniformity, preferably always halted with the images 226and 226 in the same direction from the centers of said wobble circles.

The apparatus 30 has now been completely adjusted and the automobile 221and the apparatus brought into a proper relationship for commencing tocheck the alignment characteristics of the front of dirigible wheels 220and 220' and also those of the rear or drive wheels 222 and 222. Thechecking of these two pairs of wheels may be done in any order desired,that is, the front wheels may be checked first and then the rear wheels,or the rear wheels may be checked first and after that the front wheels.

The steps involved in the checking of the alignment characteristics ofthe front wheels from this point on in performing the process of thisinvention are identical with the corresponding steps employed forchecking the alignment characteristics of dirigible vehicle wheelsdisclosed in the aforesaid U. S. Patent Number 2,470,090. A briefdescription of this follows:

Checking dirigible wheels With the apparatus set as above described, thealignment characteristics of the dirigible wheels are preferably checkedin the following order: camber, toe-in or toe-out, steering geometry,and caster. The first three of these characteristics are checked bycamber charts 240 and 240 projected on the screens 70 and 70, the chart240 being illustrated in Fig. 28. The projection of the chart 240 on thescreen 70 by the optical unit 47 is accomplished by rotating the knurledhead 85 (see Figs. 5 and 6) so as to lower the slide 81 to its lowermostposition in the slideway 80 until this will bring the camber chart film89 into the projection path of the projector 67 and cause chart 240 tobe projected in its proper position on the screen 70. This position issuch that Where there is a zero amount of camber in the dirigible wheel220, and with the latter turned straight ahead, the cross hair image 226will fall on the horizontal zero line of chart 240. Any positive ornegative camber in the wheel 220 however will be correctly indicated indegrees by the appearance of the cross hair image 226 below or above thezero line of the chart 240. The position of the cross hair image 226 onthe chart 240 in Fig. 28 indicates that the wheel 220 has a positivecamber of 1".

In a similar manner, the actual camber of dirigible wheel 220' isindicated by the position of the cross hair image 226 on the camberchart 240 which is projected on the screen 70'.

Before checking toe-in or toe-out of the wheels 220 and 220' these areagain raised by jacks 40 and 40' and rotated. These wheels are thenlowered with the cross hair beam images 226 and 226' at points half waybetween the horizontal extremes of their respective wobble circles.

To check toe-in or toe-out of the wheels 220 and 220', these are nowturned by the steering mechanism of the automobile 221 so that the crosshair image 226' falls on the vertical zero line in the toe-in section ofthe camber chart 240. By reference now to the camber chart 240 as shownin Fig. 28, the toe-in or toe-out characteristic of the wheels 220 and220' may be read by the location of the cross hair image 226 on thechart 240. In this view, an actual toe-in of one quarter of an inch iscorrectly indicated.

To check the steering geometry of the wheels 220 and 220, the operatormerely rotates the steering wheel to turn the wheels 220 and 220 abouttheir king pins so that the cross hair image of the wheel on the outsideof the turn'rests on the vertical 20 line of the caster chart of thatwheel. The operator is then able to read the actual angle at which thewheel on the inside of the turn is turned about its king pin, by theposition of the cross hair image on the caster chart of said insidewheel.

By virtue of the small size of the camber chart 240, it is not necessaryto occupy the entire area of the screen 70 by this chart, and the film89 thus provides an area 243 on which advertising material orinstructions may be placed and which will be projected on the screen 70alongside the chart 240.

The apparatus 30 and automobile 221 are at this time also properlyarranged for checking the caster of front Wheels 220 and 220'. Thecaster of the Wheel 220 is checked entirely independently from thecaster of the wheel 220. As these two operations are identical, adescription of one will suffice for both. To check caster on the wheel220, the knurled head 85 is rotated to elevate the slide 81 to bring thecaster chart film 91 into the projection path of the projector 67. Thiswill cause the projector 67 to project onto the screen 70 a caster chart241 as shown in Fig. 29. The wheel 220 is now angled to turn this to theleft until the cross hair image 226 is located on the vertical 20 lineof this chart. This indicates that the plane of wheel 220 is turnedoutward exactly 20 from straight ahead and the mirror 192 is nowautomatically substituted in place of the mirror 191 of the wheel mirrorfor intercepting and reflecting the beams 225 and 227 which form thecross hair image 226 and locator image 228. With the cross hair image226 thus located with. reference to the caster chart 241, the knurledhead 85 is rotated to adjust the caster chart film 91 vertically tocause the cross hair image 226 to fall (2)191 the horizontal zero lineof this chart as shown in Fig.

The wheel 220 is now angled inwardly until the cross hair image 226leaves the field of the chart 241, reappears to cross this chart againand disappear, and then again reappears on the chart and comes intoalignment with the 20 vertical reference line of chart 241 as shown inFig. 30. The position of the cross hair image 226 on this line will nowindicate the caster of the wheel 220 in positive or negative degrees.The caster as indicated in Fig. 30 is positive 4 and 30'.

The caster of the wheel 220 is now checked in the same manner by theright hand apparatus section 31.

Checking drive wheels With the automobile 221 positioned on theapparatus 30 as shown in Fig. 2 and wi.h the wheel mirrors applied andthe optical units 47 and 47 properly located relative to the front wheelmirrors 150 and 150', the method of the invention is adapted to beemployed as follows in checking the alignment characteristics of therear drive wheels 222 and 222.

The first steps in checking the alignment of the rear Wheels are ofcourse the projecting of the beams 112 and 113 in parallel relation withthe beams 112 and 113' respectively (and extending alongside theautomobile 221) and locating the light units 47 and 47' so that theseare equidistant laterally from point 229 in the fore and aft axis 230 ofautomobile 221 (Fig. 19) where this axis intersects a vertical planepassing through the centers of the wheels 220 and 220, and then causinga relative rotative movement between the beams and the automobile in ahorizontal plane about said point to bring the vertical plane of thebeams 112 and 113 and the vertical plane of the beams 112' and 113' intoparallelism with said automobile axis and equidistant laterallytherefrom. The manner of accomplishing these steps has already beendescribed.

It is necessary now to shift the chart film slides 81 and 81' of theprojectors 47 and 47 to bring the drive wheel chart films 90 and 90 intothe projection paths of said units so as to project drive wheel checkingcharts 245 and 245' respectively onto the screens 70 and 70'. As alreadynoted, the light beams 113 and 113 impinge upon the mirror elements 206and 206' of the drive wheel mirrors 151 and 151' and are reflectedtherefrom onto the screens 70 and 70' so as to project cruciform beamimages 224 and 224'. By rotational adjustment of the mirrors 151 and151' on their respective shafts 200 and 200', the beam images 224 and224 are now brought onto the charts 245 and 245 in selected verticalpositions thereon, which, according to the indicia 246 appearingalongside each of these charts, correspond with the wheel base of theautomobile 221. As noted in Figs. 20, 22 and 24, the divisionsrepresenting a given amount of toe-out or toe-in on the horizontal lineson charts 245 and 245' progressively increase from the upper to thelower limits of these charts. The divisions on each of these horizontallines are suitable for measurement of the amounts of toe-out or toe-innumerically indicated at the upper edge of these charts for a wheel baseof a given length. As the wheel base increases in length, it requires alarger horizontal distance on the chart to indicate a given amount oftoe-out or toe-in a rear wheel of the automobile being tested. Each ofthe indicia 246 indicates a wheel base of a certain length and isdisposed opposite the horizontal lines of the charts 245245' upon whichthe images 224-224 should be projected in order to give a correctreading of toe-out or toe-in for a car having that wheel base.

For instance, as the wheel base of the automobile 221 is approximately118 inches, the operator projects the images 224 and 224' onto thecharts 245 and 245' just above the horizontal lines on these chartswhich, according to the indicia 246, correspond to a wheel base of 120inches. This is necessary for the reading on the charts 245 and 245 tobe correct because the longer the wheel base of the automobile beingtested, the greater the distance the mirrors 151 and 151 are locatedrearwardly from the screens 70 and 70 and from the optical units 47 and47' and thus the greater the distance which the beam images 224 and 224'will fall to one side or the other of the vertical zero lines of thesecharts for a given degree of deflection from true alignment of the drivewheels 222 and 222'.

The next step in checking the alignment of the drive wheels is tosuccessively jack up the rear corners of the automobile 221 and makecorrection of the positions of the beam images 224 and 224' which arenecessary to eliminate lateral deflections due to one or both of thedrive wheels being bent so that the plane of the wheel is out ofperpendicularity to the axis of the wheels rotation. For the wheel 222,this is done by jacking up the left rear corner of the automobile 221,loosening the screw 205 of the mirror 151 and while holding this mirrorso as to keep the beam image 224 on the chart 245, rotating the wheel222 a full revolution and noting the extremes of movement of the image224 on the chart 245 to the' left and to the right. The wheel 222 isthen stopped at a position in which the image 224 is at the midpointbetween said extremes. The left rear corner of the automobile 221 is nowlowered so that the wheel 222 will again rest on the wheel track 33. Theposition of the beam image 224 on the chart 245 will now correspond towhat it would be if the wheel 222 were not bent but, instead, wereperpendicular to its axis of rotation.

The same thing as just described is now done with the right drive wheel222' while the right rear corner of the automobile 221 is temporarilyelevated.

When the foregoing steps have been completed, it is possible todetermine the alignment characteristics of the axes of rotation of therear drive wheels 222 and 221 by reading the positions of the beamimages 224 and 224' on the charts 245 and 245' and by reading the spiritlevels 210 and 210.

Figs. 19 and 20 diagrammatically illustrate positions of the beam images224 and 224' on the charts 245 and 245' which show the axes of rotationof the wheels 222 and 222' to lie in a vertical plane which isperpendicular to the fore and aft axis 230 of the automobile 221.Assuming that there is no vertical or horizontal distortion of the rearaxle housing 250, and that the wheels 222 and 222 thus rotate coaxially,the check illustrated in Figs. 1 and 20 indicates perfect alignment ofthe wheels 222 and 222'.

The checking of these wheels to see whether these are bent out ofperpendicularity with their respective axis of rotation may haveindicated oneor both wheels so affected. Nevertheless, in the absence ofa rear axle housing defect, the appearance of the images 224 and 224 onthe central vertical zero lines of the charts 245 and 245 indicates thatwhen any bent condition is eliminated from the wheels 222 and 222',these will have true coaxial rotation in parallel planes about an axiswhich is at right angles to the fore and aft axis 230 of the automobile221.

Figs. 21 and 22 illustrate a check on the drive wheels 222 and 222' inwhich the beam images 224 and 224 both fall to one side of the centralvertical zero lines of the charts 245 and 245. This discloses that theentire rear axle unit embracing the housing 250 and the drive wheelsmounted thereon has rotated about a vertical axis so that the wheel 222is shifted forwardly relative to the frame of the automobile, and thewheel 222' has shifted rearwardly relative to said frame. Thus while thewheels 222 and 222' may still rotate coaxially on the housing 250, theaxis of their rotation is not perpendicular to the fore and aft axis 230of the automobile 221, but as shown in Fig. 21 and indicated on thecharts in Fig. 22, is turned toward the right. That is, the left drivewheel 222 toes in and right drive wheel 222 toes out a correspondingamount. The actual distance of deflection of these wheels relative tothe frame of the automobile is measured on the charts 245 and 245' bythe indicia appearing along the upper edges of these charts. Thus inFig. 22, the wheel 222 is shown as being shifted one-eighth of an inchforwardly from its true position on the frame of the automobile and thewheel 222 is shown as being shifted oneeighth of an inch rearwardly fromits true position on the frame. Figs. 23 and 24 illustrate a check ofthe drive wheels 222 and 222 in which a distorted housing 250 isindicated, the distortion being in a horizontal plane so that both ofthese wheels toe out.

Figs. 25 and 26 illustrate the manner in which a distortion of thehousing 250 in a vertical plane may be detected by readings of thespirit levels 210 and 210' after the apparatus 30 has been set up inproper relation to the automobile 221 and correction made for either ofthe wheels 222 and 222' being bent as aforesaid. The levels 210 and 210have suitable calibrations by which the deflection in a vertical planeof the axes of rotation of the drive wheels from true coaxial alignmentmay be read.

An outstanding advantage of the present invention 15 that therelationship of the cross hair image and the locator beam image, whichindicates the correct spacing between the optical unit producing theseimages and the adjacent dirigible wheel mirror, is not distorted byexcessive camber in the dirigible Wheel on which said mirror is mountedas happens in certainprevious optical wheel aligners, such as thatdisclosed in the aforesaid U. S. Patent No. 2,470,090, particularly,when said dirigible wheel is being tested for caster. This freedom isbrought about by projecting the cross hair beam and locator beam in thesame plane as they approach the wheel mirror so that they strike thismirror on the same horizontal level. Excessive camber, therefore, as inthe dirigible wheel 220 for instance, does not introduce any substantialchange in the respective lengths of the paths traveled by the beams 225and 227, on their way to the screen 70, when the wheel 220 is beingchecked for caster.

Projecting beams 225 and 227 in the same horizontal plane, so that thesebeams meet at a point located in the plane of the mirror 191 when theunit 47 has been moved into the proper spaced relation with the mirror,has the effect of reducing distortion, simplifies the construction andoperation of the apparatus 30, and permits dirigible wheels of a largevariety of diameters to be checked with a wheel mirror, such as thewheel mirror 150, in which the reflecting mirrors are relatively smallin area.

Whereas no scales have been shown for use in making an exact reading ofthe angle which the plane of a bent wheel has with respect to its axis,either in the dirigible wheels or in the drive wheels of an automobile,these angles are readily determinable from the diameter of the wobblecircle produced by a dirigible Wheel, and by the distance betweenopposite extremes of movement of a rearward beam image, such as theimage 224, when the drive wheel producing this image is rotated.

A reading of said angle in a drive wheel may also be made by observingthe extremes of movement of the bubble in a spirit level (such as thelevel 210) of the drive wheel mirror mounted on this wheel, while thelatter is being rotated to see whether or not it is bent.

From the disclosure embracing the accompanying drawings and the abovedescription, it is believed clear that the present invention provides anovel and extremely efficient method and apparatus by which thealignment characteristics of all four wheels of an automotive vehiclemay be readily checked and that this may be accomplished in a relativelyshort time. It is also believed evident that the significance of thetest will be manifest to an unskilled observer so that the average carowner will be assured of the correctness of the diagnosis of thealignment characteristics of his automobile before work is started on itand be likewise assured by a recheck after the work is completed thatthe errors in alignment discovered by the first check have beencorrected.

Whereas the invention as disclosed herein is especially adapted forchecking the alignment characteristics of two front dirigible wheels ofa vehicle and two, rear, non-dirigible, drive wheels of said vehicle itis to be understood that in its broader application, the invention is byno means restricted in use to these specific operations.

It is to be further understood that while the front wheels of anautomotive vehicle are ordinarily dirigible and the rear wheelsnon-dirigible and employed to drive the vehicle, the rear wheels mightbe made dirigible and the front wheels employed to drive the vehicle andeven be made non-dirigible, but the invention is readily adaptable tochecking the alignment characteristics of such wheels by application ofthe principles disclosed herein.

It is therefore to be understood, where reference is made in the claimsto checking operations performed on rear wheels or drive wheels, theseterms are to be broadly construed as covering any non-dirigiblesupporting wheels of the vehicle whether idle or driven and no matterwhere these may be placed along the sides of the vehicle.

Whereas the most sensitive action in the opposite horizontal shifting ofimages 226 and 228 is secured by beams 225 and 227 being projectedforwardly and inwardly, and rearwardly and inwardly, respectivelyagainst mirror 191, it is to be understood that a less sensitive andtherefore less desirable action may be produced by directing both ofsaid beams forwardly and inwardly or rearwardly and inwardly againstsaid mirror along converging paths and in the same plane.

It also should be pointed out that while it is preferable to bring thelight beams 112 and 112 into parallelism with each other and with thevehicle axis 230 and equidistant from the latter, many benefits of theinvention may be realized without conforming to all these conditions.

For instance, it is important that beams 112 and 112 be substantiallyparallel with each other, that they do not diverge too much fromparallelism with the horizontal plane of the axis 230, and that thesebeams travel in parallel vertical planes. Various lateral measurementsof value may be made by the use of said beams under these conditionseven though the vertical planes aforesaid are not spaced equidistantlaterally from vehicle axis 230, so long as allowance be made for thedifferent lateral spacing of said planes.

It is likewise important that the light beams 113 and 113 besubstantially parallel and lie in the same parallel vertical planes inwhich beams 112 and 112' travel. They preferably come from the samerespective sources and thus diverge upwardly at slight angles from beams112 and 112. Nevertheless beams 113 and 113 could accurately performtheir functions of indicating the toe-in and toe-out of the rear vehiclewheels 222 and 222 even though the parallel vertical planes containingsaid beams are not equally spaced laterally from vehicle axis 230.

In the preferred embodiment of the invention above described, theprojection base is mounted for rectilinear movement towards or away fromthe wheel mirror along a path which is parallel with a line passingthrough the centers of the dirigible wheels when the latter are turnedstraight ahead. To simplify the definition of this line in the claims,it will be assumed without mention being made thereof, that the wheelsare turned straight ahead when their centers determine this line. Itshould also be noted that while the direction of movement of theprojection base is preferably parallel with said line, deviation fromparallelism is possible so long as said direction has a fixedorientation relative to said line.

The present application is a division of my co-pending applicationSerial No. 659,317 filed April 3, 1946, now Patent No. 2,601,262, forMethod of and Apparatus for Measuring Alignment Characteristics of Frontand Rear Wheels.

Having thus described my invention what I claim as new and desire toprotect by Letters Patent is:

1. An apparatus for measuring an alignment characteristic of a dirigiblewheel comprising a mirror mounted on the wheel and having a reflectingsurface facing laterally therefrom in a plane having a fixedrelationship to the plane of the wheel, a screen mounted in spacedrelation to said mirror and adapted for receiving images, primary lightsource means arranged to project a first beam of light against saidmirror, secondary light source means arranged to project a second beamof light against said mirror at a different angle than said first beambut in the same plane, and reflector means lying in the paths ofreflection of said light beams, said reflector means being arranged toagain reflect said light beams to cause the latter to project imagesupon said screen, said light source means and reflector means beingmounted for movement as a unit toward and away from said wheel to causea variation in the positional relation of said images on the screen andthe attainment of a particular positional relation between said imageson said screen when a certain desired spacing of said light source meansand reflector means from said wheel has been accomplished.

2. An apparatus for measuring an alignment characteristic of a dirigiblewheel disposed on a support surface comprising a mirror mounted on awheel and having a reflecting surface facing laterally therefrom in aplane having a fixed relationship to the plane of the wheel, a fiatscreen spaced from said mirror and adapted to receive images, an opticalunit disposed laterally from the reflecting surface of said mirror,means for mounting said unit for adjustable movement toward or away fromsaid mirror, means in said optical unit for projecting two beams oflight at different angles towards the refleeting surface in a horizontalplane, and reflectors on said unit arranged to intercept the two beamsof light reflected from said mirror and direct said reflected beams ontosaid screen, said reflectors and said beams projecting means being soarranged that images of said beams on said screen travel in oppositedirections when said unit is shifted toward or away from said mirror, agiven positional relationship between said images on said screenindicating a predetermined spacing of said unit from said mirror.

3. An apparatus for measuring an alignment characteristic of a dirigiblewheel disposed in an inclined position on a support surface comprisingan optical unit, means for mounting said optical unit for movementlaterally toward and away from said wheel, a screen disposed apredetermined distance from said optical unit, a mirror mounted on saidwheel facing laterally therefrom and disposed in a plane having a fixedrelationship with the plane of said wheel, a chart projector on saidunit for projecting a calibrated chart on said screen, light sourcemeans on said unit for projecting light beams inwardly and forwardly andinwardly and rearwardly from said unit against said mirror in a planeparallel to the wheel support surface, and reflecting means on said unitfor receiving said beams when the latter are reflected from said wheelmirror and directing said beams onto said screen, said light sourcemeans and said reflectors being so disposed that images of said beamstravel in opposite directions on said screen when said unit is shiftedtoward and away from said wheel mirror, a given positional relationshipbetween said images on said screen indicating a predetermined spacing ofsaid unit from said wheel mirror, said chart projector having means forso locating said chart as to cause the image of one of said beams, whenprojected thereon with said unit so spaced, tohinilicate a particularalignment characteristic of said w ee 4. In an apparatus for measuringan alignment characteristic of a dirigible wheel, the combination of, amirror mounted on said wheel facing laterally therefrom, said mirrorhaving a fixed relationship with the plane of said wheel, a screen forreceiving images, primary light source means for projecting a first beamof light forwardly and inwardly in a horizontal plane against saidmirror, secondary light source means projecting a second beam of lightrearwardly and inwardly against said mirror in the horizontal plane onsaid first beam, and reflector means lying in the paths of reflection ofthe aforesaid light beams, said reflector means again reflecting saidlight beams to cause the latter to project images upon said screen, saidlight source means and reflector means being mounted for movement as aunit toward and away from said wheel, to cause a variation in thepositional relation of said images on said screen and the attainment ofa particular positional relation between said images when a certaindesired spacing of said light source means and reflector means from saidwheel has been accomplished.

5. An apparatus for measuring the caster of a dirigible wheel comprisinga pair of mirrors mounted on said wheel at opposite sides of the centralaxis thereof and angled relative thereof, a base mounted for rectilinearmovement toward and away from said mirrors in a direction having a fixedorientation relative to the central axis of said wheel with the latterturned straight ahead, a screen spaced from said base and disposed toreceive light images thereon from said base, optical means on said basefor projecting a pair of converging beams of light towards said mirrors,one a cross hair beam, and the other, a locator beam, said beams lyingin a common plane, each of said beams having a fixed orientationrelative to the direction of movement ofsaid base, reflector meansprovided on said base and lying in the paths of the reflections of saidlight beams from said mirrors and having a fixed angular relation withsaid direction of movement to deflect said reflected beams on to saidscreen whereby a cross hair image is produced by one beam and a locatorimage is produced by the other beam, so that when said base is shiftedin said direction to bring about a predetermined relation on said screenbetween said cross hair and said locator images a predetermined spacedrelationship will have been accomplished between said base and saidmirrors, and means providing a caster chart on said screen, said charthaving calibrations which indicate quantitatively the amount of casterof said wheel by virtue of the distance traversed on said caster chartby said cross hair image when said wheel is swung between apredetermined position pointing toward the base in which one of saidmirrors is exposed to said beams, and a corresponding predeterminedposition pointing away from the base in which the other of said mirrorsis exposed to said beams, the coplanar relationship of said convergingcross hair and locator beams resulting in the maintenance of the imagethereof on said screen in said predetermined relation during saidswinging of the wheel regardless of the camber thereof.

6. A combination as in claim 5 in which said screen is disposedvertically and is substantially parallel with said direction, in whichsaid direction is substantially parallel with the central axis of saidwheel when the latter is turned straight ahead, and in which the planein which said light beams are projected toward said mirrors ishorizontal.

References Cited in the file of this patent UNITED STATES PATENTS

